1. Field of the Invention
This invention relates to cam grooves for an optical system such as a zoom lens system or a super-telephoto lens system, wherein at least more than two lenses, or two or more lens groups, are displaced in parallel to an optical axis.
2. Description of the Prior Art
In a zoom lens, one or more lenses or one or more lens groups of a plurality of lens groups which constitute the zoom lens must be displaced, in order to maintain a focusing plane usually constant, even with a change of a focal length. The state of displacement of such lenses varies, because the lengths of displacement of such lenses are determined in a manner that various aberrations in a train of focal lengths in permissible focal range do not cause an undesired influence.
Particularly in a super-telephoto lens, system, if all of the lens groups are displaced, as an aerial space between lens groups remains consistent, in order to focus the lenses, then large lengths of displacement of such lenses result. To cope with this, it has been customary to displace one or more lens or one or more lens groups of the plural lens groups in order to diminish the lengths of displacement of the lenses and reduce a macro-photographic distance. The states of displacement of such lenses are various, in order to maintain constant various factors such as chromatic aberration, etc.
The states of displacement of such lenses are defined, on the optical design, as a train of displacements in the permissible focal range, namely, as focal lengths in a zoom lens and as a photographic distance in a super-telephoto lens system. Cam grooves in an optical system are designed by making an angle of rotation about an optical axis or a length of displacement parallel to the optical axis, of a lens operating member properly correspond to a changing focal length or photographic distance. A configuration of a cam groove is thus dependent on a degree of displacement, or an angle of rotation about an optical axis, of the lens operating member corresponding to a changing focal length or photographic distance.